Passing Claims through a web front end to a WCF service

I've been working on a disconnected WCF system with a web front end that needs to authenticate against a RP using Windows Identity Foundation. The basic setup is as follows;

RP (+ claims) -> Web Front End -> WCF Services(~)

The WCF need to make sure that the user logged in is on the RP and has the claims required to do particular actions.

I am having problems calling the WCF service from the Web Front End and still having the authorisation and claims, originally retr开发者_如何转开发ieved from the RP, available.

Basically, I can't access the RP claims from the WCF when the WCF is called by the web front end.